1. Field of the Invention
The present invention relates to an optical information recording medium in which two types areas, that is, areas in guide grooves formed on the optical information recording medium in advance and areas between guide grooves, are used as information recording tracks, and an optical information recording/reproducing apparatus for recording information signals in the optical information recording medium.
2. Description of the Related Art
In recent years, the development of optical information recording media capable of recording/reproducing information signals such as video or audio signals goes on increasing. Optical disk is one of the optical information recording media. In a recordable optical disk, guide grooves are formed in an optical disk substrate to thereby form tracks. Laser light is converged to flat portions of concave or convex portions among the tracks to thereby perform recording/reproducing of information signals. In a general optical disk which is available currently, either concave portions or convex portions are generally used for recording information signals but the other concave or convex portions are used as guard bands for separating adjacent tracks.
FIG. 39 is an enlarged perspective view of such a conventional optical disk. In the drawing, the reference numeral 201 designates a recording layer which is, for example, formed from a phase change material. The reference numeral 202 designates recording pits; and 203, a beam spot of laser light. The reference numeral 204 designates concave portions formed from guide grooves; and 205, convex portions between guide grooves. The width of each of the concave portions 204 is set to be larger than the width of each of the convex portions 205. The reference numeral 206 designates pre-pits which form identification signals expressing position information on the disk. In the drawing, a transparent disk substrate which transmits incident light is not shown.
A conventional optical information recording/reproducing apparatus using this type optical disk will be described below with reference to the drawings.
FIG. 40 is a block diagram of the conventional optical information recording/reproducing apparatus. In the drawing, the reference numeral 207 designates an optical disk; and 208, a recording track which is constituted by a concave portion 204 in this case. The reference numeral 210 designates a semiconductor laser; 211, a collimator lens for collimating laser light emitted from the semiconductor laser 210; 212, a half mirror arranged on a light bundle; and 213, an objective lens for converging collimated light passing the half mirror 212 onto a recording surface of the optical disk 207. The reference numeral 214 designates a photo detector for receiving light passing through the objective lens 213 and the half mirror 212 and reflected from the optical disk 207. The photo detector 214 is divided into two parts in parallel with the track direction of the disk in order to obtain a tracking error signal. That is, the photo detector 214 is constituted by two light-receiving portions 214a and 214b. The reference numeral 215 designates an actuator for supporting the objective lens 213. These parts are mounted on a head base not shown to form an optical head 216. The reference numeral 217 designates a differential amplifier which receives detection signals outputted from the light-receiving portions 214a and 214b; and 218, a low pass filter (LPF) which receives a differential signal outputted from the differential amplifier 217. The reference numeral 219 designates a tracking control circuit which receives the output signal of the LPF 218 and a control signal L1 from a first system controller 232 and gives a tracking control signal to a driving circuit 220 and a traverse control circuit 226. The reference numeral 220 designates a driving circuit for giving a driving current to the actuator 215. The reference numeral 221 designates an addition amplifier which receives detection signals outputted from the light-receiving portions 214a and 214b and generates a summation signal; 222, a high pass filter (HPF) which receives the summation signal from the addition amplifier 221 and delivers high-frequency components of the summation signal to a waveform shaping circuit 223; 223, a first waveform shaping circuit which receives high-frequency components of the summation signal from the HPF 222 and delivers a digital signal to a reproduction signal processing circuit 224 and a first address reproducing circuit 225; and 224, a reproduction signal processing circuit which delivers an information signal such as an audio signal to an output terminal 233. The reference numeral 225 designates a first address reproducing circuit which receives the digital signal from the first waveform shaping circuit 223 and delivers an address signal to a first system controller 232. The reference numeral 226 designates a traverse control circuit which gives a driving current to a traverse motor 227 on the basis of a control signal L2 given from the first system controller 232; and 227, a traverse motor for moving the optical head 216 in the direction of the radius of the optical disk 207. The reference numeral 228 designates a spindle motor for rotating the optical disk 207. The reference numeral 229 designates a recording signal processing circuit which receives an information signal such as an audio signal from an external input terminal 230 and delivers a recording signal to a laser driving circuit 231; and 231, a laser driving circuit which receives a control signal L3 from the first system controller 232 and the recording signal from the recording signal processing circuit 230 and gives a driving current to the semiconductor laser 210. The reference numeral 232 designates a first system controller which delivers control signals L1 to L3 to the tracking control circuit 219, the traverse control circuit 226 and the recording signal processing circuit 229 and receives the address signal from the first address reproducing circuit 225.
The operation of the conventional optical information recording/reproducing apparatus configured as described above will be described below with reference to the drawing.
A laser beam radiated from the semiconductor laser 210 is collimated by the collimator lens 211 and converged onto the optical disk 207 by the objective lens 213 via the beam splitter 212. The light beam reflected from the optical disk 207 carries information of recording track 208 by diffraction and is led onto the photo detector 214 by the beam splitter 212 via the objective lens 213. The light-receiving portions 214a and 214b convert the changes of the light quantity distribution of the incident light beam into electric signals and deliver the electric signals to the differential amplifier 217 and the addition amplifier 221. The differential amplifier 217 subjects the respective input currents to I-V conversion, calculates difference between voltage values and delivers the difference signal as a push-pull signal. The LPF 218 extracts low-frequency components from the push-pull signal and delivers the low-frequency components as a tracking error signal to the tracking control circuit 219. The tracking control circuit 219 gives a tracking control signal to the driving circuit 220 in accordance with the level of the input tracking error signal, so that the driving circuit 220 supplies a driving current to the actuator 215 in accordance with the tracking control signal to thereby control the position of the objective lens 213 in the recording track-crossing direction. As a result, the beam spot performs scanning on the convex portion 205 correctly. On the other hand, the position of the objective lens 213 is controlled in the direction perpendicular to the disk surface by a focussing control circuit not shown in order to focus the beam spot onto the disk correctly.
On the other hand, the addition amplifier 221 subjects the output currents of the light-receiving portions 214a and 214b to I-V conversion, adds voltage values and delivers the resulting signal as a summation signal to the HPF 222. The HPF 222 cuts off unnecessary low-frequency components from the summation signal, makes the reproducing signal as a main information signal and the address signal pass in analog waveform and delivers the signals to the first waveform shaping circuit 223. The first waveform shaping circuit 223 performs data slicing of the analog waveform main information signal and address signal by a predetermined threshold to form a pulse waveform and delivers the pulse waveform to the reproducing signal processing circuit 224 and the first address reproducing circuit 225. The reproduction signal processing circuit 224 decodes the input digital main information signal, applies processes such as error correction to the decoded signal and delivers the resulting signal as an audio signal or the like to the output terminal 233. The first address reproducing circuit 225 decodes the input digital address signal and delivers the decoded signal, as information of position on the disk, to the system controller 232. That is, as a result of scanning of the beam Spot 203 on recording pits 202, a reproducing signal is given to the reproduction signal processing circuit 223, and as a result of scanning on pre-pits 206, an address signal is given to the first address reproducing circuit 225. The first system controller 232 judges on the basis of the address signal whether the light beam is currently fit to the desired address.
The traverse control circuit 226 gives a driving current to the traverse motor 227 in accordance with the control signal L2 given from the first system controller 232 at the time of transferring of the optical head to thereby move the optical head 216 to the target track. At this time, the tracking control circuit 219 temporarily interrupts tracking servo on the basis of the control signal L1 given from the first system controller 232. Further, at the time of ordinary reproduction, the traverse motor 227 is driven in accordance with low-frequency components of the tracking error signal given from the tracking control circuit 219 to thereby move the optical head 216 slowly in the direction of the radius of the disk with the advance of reproduction.
The recording signal processing circuit 229 adds an error code or the like to an audio signal or the like inputted from the external input terminal 230 at the time of recording and delivers the resulting signal as a coded recording signal to the laser driving circuit 231. When the first system controller 232 sets the laser driving circuit 231 to a recording mode through the control signal L3, the laser driving circuit 231 modulates a driving current to be applied to the semiconductor laser 210 in accordance with the recording signal. As a result, the intensity of the beam spot radiated onto the optical disk 207 changes according to the recording signal, so that recording pits 202 are formed. On the other hand, at the time of reproduction, the laser driving circuit 231 is set to a reproducing mode through the control signal L3, so that a driving current is controlled to emit light from the semiconductor laser 210 at constant light intensity. As a result, recording pits or pre-pits on recording tracks can be detected.
While the respective operations as described above are carried out, the spindle motor 228 rotates the optical disk 207 at a constant angular velocity.
Conventionally, in order to increase the recording capacity of the optical disk 207, the width of the convex portion 205 is narrowed so that the distance between tracks is reduced. When the distance between tracks is reduced, however, the diffraction angle of reflected light due to the concave portion 203 becomes large. Accordingly, there arises a problem in that the tracking error signal for making the beam spot 203 follow a track with high accuracy is lowered. Further, because there is a limit to the attempt to reduce the distance between tracks only by narrowing the width of the convex portion 205, the width of the concave portion 204 must be narrowed. As a result, the size of the recording pits 202 is reduced, so that there arises a problem in that the amplitude of the reproducing signal is lowered.
On the other hand, there is a technique of recording information signals both in concave portions 204 and in convex portions 205 to thereby increase track density, as described in JP-B-63-57859.
FIG. 41 is an enlarged perspective view of such an optical disk. In the drawing, the reference numeral 201 designates a recording layer; 202, recording pits; and 203, a beam spot of laser light. Like numerals in each of FIGS. 39 and 41 refer like parts. The reference numeral 240 designates concave portions formed as guide grooves; and 241, convex portions between guide grooves. As shown in the drawing, the width of each of the concave portions 240 is set to be substantially equal to the width of each of the convex portions 241. The reference numeral 242 designates pre-pits which are formed both in the concave portions 240 and in the convex portions 241 and placed in the respective heads of sectors in the two types of recording tracks so as to serve as identification signals expressing information of position on the optical disk.
In the optical disk, the recording pits 202 are formed both in the concave portions 240 and in the convex portions 241 as shown in the drawing. The guide groove pitch of the operational disk in FIG. 41 is equal to that of the optical disk in FIG. 39, but the distance between recording pit trains is reduced to 1/2. As a result, the recording capacity of the optical disk is increased to two times. Hereinafter, the concave portions 240 and the convex portions 241 in this type optical disk are generically called "recording tracks" in the meaning that recording pits 202 are formed.
The recording/reproducing operation of the optical information recording/reproducing apparatus for recording information signals in this type optical disk is carried out substantially in the same manner as the conventional optical information recording/reproducing apparatus shown in FIG. 40. However, as described in JP-B-63-57859, it is necessary that the polarity of the tracking error signal when the beam spot 202 performs scanning on the convex portion 241 is inverted to the polarity of the tracking error signal when the beam spot 202 performs scanning on the concave portion 240. This can be realized by inserting an on/off controllable inversion amplifier in between the LPF 218 and the tracking control circuit 219 in FIG. 40.